At present, in communication terminals such as a personal computer (PC), a cellular phone, and a smartphone, user-to-user communication is performed by various communication means. Examples of the communication means include e-mail, a voice call, a video call, chatting, and the like. Users start user-to-user communication by identifying desired communication means. In this manner, current communication terminals determine the type of communication means in advance of the start of user-to-user communication. Thus, there is a problem in that the current communication terminals are not able to switch the type of communication means without terminating the user-to-user communication.
Consequently, the following Patent Document 1 proposes a method that enables to switch the type of communication while continuing communication. Specifically, in the following Patent Document 1, a terminal device, which has received a request for a change in the type of communication from a user in a communication phase after the beginning of the communication, performs transmission control by adding data for requesting switching of the communication type to control data (SA of TCH data). The terminal device, which has received the switching request, performs switching control so that communication according to the request can be performed, when the data for requesting switching of a communication type is included in a received signal in the communication phase.